The present invention relates to the method of preparing peracetic acid.
One of the best-known oxidation agents is peracetic acid, especially for the preparation of epoxides or lactones from ketones via the Baeyer-Villiger reaction.
Peracetic acid is generally prepared in a classical manner by reacting acetic acid with hydrogen peroxide in the presence of an acidic catalyst, usually sulfuric acid. More or less pure aqueous solutions of peracetic acid accumulate thereby, depending on the type of performance, such as, for example, the so-called equilibrium peracetic acid consisting of approximately 40-42% peracetic acid, 37-40% acetic acid, 10-14% water, 4-6% hydrogen peroxide and 0.5-1% sulfuric acid. ("Ullmann's Enzyklopadie der technischen Chemie", 3d edition, vol. 13, p. 254)
Very pure aqueous solutions are obtained if a reaction mixture is used which contains, in addition to water and the acidic catalyst, more than 1 mole hydrogen peroxide per mole acetic acid and if the peracetic acid is distilled off under reduced pressure with water, cf. loc. cit., Supplementary Volume, 3d edition, page 181. These very pure solutions can be converted by means of azeotropic entrainer agent distillation into water-free organic peracetic acid solutions, cf. loc. cit. and DE-PS 11 65 576.
A water-free, organic solution of peracetic acid can also be obtained by azeotropically removing the water by means of the simultaneous presence of an organic solvent which forms an azeotrope with water in the reaction of hydrogen peroxide and acetic acid in the presence of an acidic catalyst, cf. Ullmann, Supplementary Volume, loc. cit.
However, there are also known industrial safety risks involved in the preparation of organic percarboxylic acid solutions. For this reason, the attempt was made to obtain the corresponding organic solutions by means of the direct extraction of aqueous mixtures of percarboxylic acid, which solutions were azeotropically dewatered by the addition of an entrainer agent. Suitable extraction agents were aliphatic, cycloaliphatic and aromatic hydrocarbons as well as chlorinated hydrocarbons, cf. DE-OS 21 45 603. Hydrogen peroxide was added as a 30 to 90% by weight, preferably as 45 to 70% by weight aqueous solution in excess over the carboxylic acid, preferably in highly concentrated, aqueous form.
Phosphoric ester, preferably trialkyl phosphates, were also used as extraction agents and the extracts obtained were then desorbed with alkyl esters of lower carboxylic acids. The percarboxylic acids used were 10-80, preferably 20-60% by weight aqueous solutions, cf. U.S. Pat. No. 3,829,216.
A moment of danger was seen only in the fact that an organic solvent was present in addition to hydrogen peroxide, percarboxylic acid and acidic catalyst and the only attempt made was to avoid this combination. It turned out, however, that the moment of danger also occurred without the presence of an organic solvent. For this reason, in particular the molar ratio of hydrogen peroxide to carboxylic acid used was set at certain values before the reaction was started. It also turned out that the safety of the system did not, as assumed, remain continuously constant after a certain value but rather that a distinct safety gap occurred within the ranges of this molar ratio used, cf. DE-OS 25 19 299 and 25 19 300. The weight ratio of hydrogen peroxide to water also played a part in this process.